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Mt. St. Helens. The Eruption.

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by

Ben Welsh

on 15 November 2013

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Transcript of Mt. St. Helens. The Eruption.

Mt. St. Helens.
Location.
Mt. St. is located in the Cascade Mountain Range, Washington State in North America. Washington and the entire of North America are MEDC countries, this means, "more economically developed countries. This means that in the case of any natural hazard or an event that requires an immediate response. Washington can get people such as builders and response teams to the scene to rescue survivors and start building again.
For example, one of the main ways that you can tell if a country is a MEDC or a LEDC is buy looking at the countriesl life expectancy, GDP per Capita and Litreracy rate.
The literacy rate is 99%, the GDP is $52,403 and the life expectancy is 78.62 years.
Causes for Eruption
There are 2 main reasons for the eruption and landslide, the first being the more important of the 2, because without this, the volcano would not have erupted until a much later date.
From a few days before the main eruption, multiple minor earthquakes went off under Mt. St. Helens, which may have loosened the north face of the mountain allowing to create the landslide when the main earthquake happend. A few minutes before the eruption, a magnitude 5.2 earthquake shook the ground, causing the landslide in this video. (if you don't want to watch the full video, skip to near the end)
Primary Effects
The main effects did not actually come from the lava and the eruption itself. The main effect came from the pyroclastic cloud and the landslide.
The landslide caused acres of the surrounding forest to be buried under a huge pile of rocks and rubble. It also claimed the lives of 57 people, 4 who weren't anywhere near the blast but were killed because of the aftereffects of the blast.
The lateral blast of the volcano caused over 209 houses to be destroyed, it also destroyed rivers and completely stopped all form of transportation anywhere near Mt. St. Helens.

Mt. St. Helens. Introduction.
At 12:36pm, on March 17 1980, Mt. St. Helens erupted. Claiming the lives of 57 people in the process. Although this particular eruption was not the deadliest, nor was it the biggest. It did have one of the biggest impacts on Americas economic society because of the amounts of flights that were grounded due to the huge pycroclastic flow Mt. St. Helens threw up.
Not only did Mt. St. Helens ground nearly every flight near the volcano, it was also the first pyroclastic flow to be monitered using modern scientific equipment, it created one of the biggest landslides in recoreded history, and it erupted laterally, which made it more dangerous to people to the north of it. But nearly perfectly safe for people to the south of the volcano.
This is Mt. St. Helens
This is Mt. St. Helens now.
As you can see, there is a huge crater where the mountain used to be
On the north side you can clearly see that this part of the mountain has fallen off and collapsed.
Phreatic Eruptions.
Phreatic Eruptions are clouds of superheated steam that shoot to the surface when a crach in the mantle allows them out. Now as you saw from the video, after the landslide, two spouts of gas shot out of the mountain, one laterally, one vertically. These created bigger holes in the mountain for the pyroclastic cloud to come out of. These eruptions also loosened the land on the mountain, allowing the huge landslide you saw.
Build up of pressure here caused
the earthquakes.

This caused the "cap" of the volcano to break, allowing the lava and pyroclastic cloud out.
It also caused the north face of the mountain
to collapse.

Plate Movement.
As you saw from that diagram, the pacific plate and the much smaller , Juan de Fuca plate are slowly drifting apart. This diverging movement is allowing magma to come to the surface and create new ocean floor. However, this is forcing the Juan de Fuca plate, under the North American plate, creating pressure as friction and heat is built up as they try to go over and under each other. This is what caused all of the earthquakes, which eventually caused the landslide, the eruption and the pyroclastic cloud.
Secondary Effects.
Although that this is the most devastating, it only happened once the eruption had taken place, and the effect was huge. When Mt. St. Helens erupted, she released what is known as a pyroclastic flow. This is a cloud that is made of fire, ash and lighting, which crippled any planes that were near it, and delayed others from even getting in the sky. However, because St. Helens erupted laterally, most of the flow was directed ate the ground.
Thankfully, because Mt. St. Helens is an active volcano, not many people live nearby. This why only 57 people died. 4 of wh died from ash inhalation.
The pyrclastic flow did however cause huge problems economic problems for a few days around Washington because no planes could take off in case their engines failed causing anyone on holiday to stay at their hotel longer and costing the hotels thousands.
Lahar?
A lahar is a destructive mud flow caused by a volcano which can destroy all habitat in an area.
Immediate Responses.
After the blast, he national guard flew in over 2 weeks to rescue survivors. They also provided clean water, medical supplies and food. they also supplied over 2 million gas masks to people in the blast area.
Ash was also cleared from most towns in under 4 days.
Long Term
Over 10 million new trees were planted, all the rivers were cleared of ash and mud, bridges were built with a larger width in case of blockages in the future and the volcano is now constantly monitered in case of another eruption and a evacuation stratagy has been devised.
All of this done by the U.S. and they did not require any other countries for help.
I hope you enjoy this presentation on Mt. St. Helens.
By Ben Welsh
Full transcript